Organic Matter Controls of Iron Incorporation in Growing Sea Ice

Abstract

This study presents the first laboratory-controlled sea-ice growth experiment conducted under trace metal clean conditions. The role played by organic matter in the incorporation of iron (Fe) into sea ice was investigated by means of laboratory ice-growth experiments using a titanium cold-finger apparatus. Experiments were also conducted to understand the role of extracellular polymeric substances (EPS) in the enrichment of ammonium in sea ice. Sea ice was grown from several seawater solutions containing different quantities and qualities of particulate Fe (PFe), dissolved Fe (DFe) and organic matter. Sea ice and seawater were analyzed for particulate organic carbon and nitrogen, macro-nutrients, EPS, PFe, and DFe, and particulate aluminum. The experiments showed that biogenic PFe is preferentially incorporated into sea ice compared to lithogenic PFe. Furthermore, sea ice grown from ultra-violet (UV) and non-UV treated seawaters exhibits contrasting incorporation rates of organic matter and Fe. Whereas, the effects of UV-treatments were not always significant, we do find indications that the type or organic matter controls the enrichment of Fe in forming sea ice. Specifically, we come to the conclusion that the incorporation of DFe is favored by the presence of organic ligands in the source solution.

Iron Incorporation From Seawater Into Antarctic Sea Ice: A Model Study

“…Imposing a constant DFe concentration in sea ice in the CST formulation assumes an instant saturation in sea ice. The continuous enrichment of DFe in young sea ice in the study of Janssens et al (2016) suggests that, aside from rapid processes such as ice nucleation or scavenging by frazil crystals, other processes also important for the incorporation of DFe into sea ice such as the role played by extracellular polymeric substances and particulate organic carbon (Janssens et al, 2018) are not accounted for by this very simplified approach. In addition, the reported variations in DFe concentrations in sea ice (de Jong et al, 2013(de Jong et al, , 2015Lannuzel et al, 2007Lannuzel et al, , 2008Lannuzel et al, , 2011Lannuzel et al, , 2016van der Merwe et al, 2011) strongly suggest that there is no saturation of the Fe storage capacity of sea ice as long as enough organic ligands are present to keep Fe in the dissolved phase.…”

“…Iron-rich waters favor Fe incorporation, in particular near sediment sources, as suggested by summer land-fast sea ice cores from the McMurdo area (de Jong et al, 2013). Dissolved Fe within brine samples is generally much lower than retrieved from melted ice core sections, which suggests the adsorption of DFe onto something within sea ice (Lannuzel et al, 2016), possibly aided by the presence of Fe-binding organic ligands such as exopolysaccharides (Janssens et al, 2018;Lannuzel et al, 2007Lannuzel et al, , 2015. This supposition is reinforced by the strong association of DFe with organic matter in sea ice, which suggests a prominent role of biology-for instance biological assimilation into growing algae or recycling by organic matter.…”

Spatial and seasonal distribution of dissolved and particulate bioactive metals in Antarctic sea ice

“…Finally, all metals analyzed here were enriched in sea ice relative to seawater when normalized to salinity (Table 4). We suggest that organic ligands, most likely EPS, are responsible for this enrichment in sea ice, as they can bind a wide range of metal cations due to their negatively charged surfaces (van der Merwe et al, 2009;Janssens et al, 2018). The high uronic acid content of EPS (Decho and Gutierrez, 2017) provides EPS with the ability to chemically complex and adsorb metals, leading us to suggest EPS as a prime pathway for organic matter and metal incorporation into newly forming sea ice.…”

Extracellular polymeric substances in Antarctic environments: A review of their ecological roles and impact on glacier biogeochemical cycles

“…The negatively charged surface of EPS (Decho, 1990;Nichols et al, 2005a) helps bind cationic metals like Fe 3+ and Fe 2+ . This together with the fact that EPS in marine systems, can be several orders of magnitude more adhesive than other particles (Passow, 2002), facilitates the attachment and adhesion of PFe in sea ice (Janssens et al, 2018;Lannuzel et al, 2016). EPS thus serves as an organic ligand that controls DFe enrichment in sea ice (Lannuzel et al, 2015).…”

“…They play an important role in the formation of biofilms on glacier surfaces, promoting efficient transfer J o u r n a l P r e -p r o o f and cycling of nutrients (Smith et al, 2016). They also contribute to mineral precipitation (Norman et al, 2015;Or et al, 2007), production of organic matter (Nichols et al, 2005a), and biogeochemical cycling of elements Janssens et al, 2018;van der Merwe et al, 2009) in the environment. EPS is not only produced by cyanobacteria and heterotrophs, but also consumed and re-assimilated by them (Stuart et al, 2016), thus fuelling the microbial web (Almela et al, 2019).…”